Heat developable light sensitive diazo compositions containing dicyandiamide



United States Patent HEAT DEVELUPABLE LlGHT SENSlTIVE DEAZO CGMPGSITKQNS CONTG DECYANDEAMEDE Claude M. Aebi and Frank W. Haining, both of Endicott,

N.Y., assignors to International Business Machines Corporation, New York, N .Y., a corporation of New York No Drawing. Filed Dec. 29, 1961, Ser. No. 163,055

7 Claims. (Cl. 96- 75) The present invention relates to light-sensitive diazonium compositions. More specifically, the invention is directed to such compositions which are heat-developable. The compositions of the invention are also notably characterized by their usefulness in the production of lightsensitive diazonium elements having good shelf life and yielding images of high resolution and great stability, even in the presence of high relative humidity atmospheric conditions.

The diazonium compositions most widely employed in conventional diazo copying devices comprises a lightdecompo-sable diazonium salt, an organic coupling component and an acid. An element coated with such a composition is exposed to light through a negative or positive and the diazonium salt is decomposed, preventing development in the exposed region. The exposed element is then treated with an alkaline developing agent, such as gaseous ammonia, which raises the pH of the film and permits the color-forming reaction to proceed between the undecomposed diazonium salt and the organic coupling component.

According to one modification of the foregoing diazo system, the organic coupling component is not initially combined with the diazonium salt, but is applied together with the alkaline medium after exposure of the diazo element.

Both of the foregoing compositions have the disadvantage of requiring a separate coupling component to produce a colored azo dye upon development. Where the coupler is initially combined with the diazonium salt, the composition is subject to premature coupling and has limited shelf life. Both of the foregoing types of composition require the application of a separate fluid to develop the image.

To obviate the requirement of a separate developing fluid, diazo compositions have been formulated which contain compounds capable of yielding alkaline developing products when decomposed by heat. Such diazo compositions, however, still require the presence of a separate coupling component in order to produce azo dyes.

In an attempt to improve upon such diazonium saltcoupler systems, use has also been made of self-coupling diazo materials. Such compositions comprise diazonium compounds or mixtures of such compounds which are capable of yielding colored compounds by reaction with their own photolysis decomposition products. In use, the materials are exposed through a negative to produce the desired positive. By controlling the extent of the exposure, the self-coupling compounds are partially decomposed and the undecomposed portion reacts with the products of decomposition to form the desired positive image in the exposed regions.

Such compositions have not gained wide acceptance because the images formed are not stable and the level of contrast between the image produced and the background is low. Also, elements of this type must he subsequently treated to destroy the remaining undecomposed diazo material on the unexposed area of the film. In addition, an alkaline developing step has also generally been required with such compositions in order to bring the color forming reaction to completion. The foregoing materials are primarily useful in negative copying processes.

Accordingly, a general object of the present invention out the presence in the system of a separate coupling component until thermally developed and without the application of a separate developing fluid.

Another object of the present invention is the provision of a light-sensitive diazonium composition that is developable by heat.

A further object of the present invention is the provision of heat-developable, light-sensitive diazonium compositions, initially containing no coupling component which yield images of a sharpness, intensity and stability not formerly obtainable with prior art materials.

Another object of the present invention is the provision of diazonium compositions which can be stored under high humidity conditions for relatively long periods of time without noticeable impairment of their usefulness.

An additional object of the present invention is the provision of diazonium compositions which may be employed in relatively simple azo copying devices, since no means for generating developing fluids or evacuating noxious by-product vapors need be provided.

Another object of the present invention is the provision of diazonium compositions which may be employed as coatings on various substrates to produce highly useful photosensitive copying papers.

The manner in which the foregoing objects and many other highly desirable objects have been achieved according to the present invention will be readily apparent in the light of the following description and claims, the description including certain detailed examples of preferred embodiments of the invention.

We have discovered that stable, heat-developable diazo compositions may be produced by combining conventional diazonium salts with dicyandiamide and an acid.

Among the diazonium salts useful in the present compositions are the following: p-diazo aniline, p-diazo N- methyl-N-hydroxyl-aniline one-half zinc-chloride, p-diazo diethylaniline borofluoride, l-N-rnorpholino 4-diazo, 5- diethoxybenzene one-half zinc-chloride salt and p-diazoethylhydroxyl-ethylaniline one-half zinc-chloride salt. The foregoing are merely examples and are not exhaustive of the light-sensitive diazonium salts useful in the present compositions.

In general, satisfactory acids for incorporation in the present compositions are polycarboxylic acids such as citric, maleic and malonic.

A composition of the present invention may be applied as a coating to various substrates, in a plurality of separate layers or films. Thus, the dicyandiamide may be dissolved and the solution coated and dried on a paper base. A solution of a diazonium salt and acid may then be applied over the first coating and dried to produce a doublecoating on the base. Or, if preferred, the dicyandiarnide,

acid and diazonium salt may all be dissolved in the same solvent and applied as a single coat on the base.

The preferred method for utilizing the compositions of the present invention comprises forming a solution containing dicyandiamide, a light-sensitive diazonium salt, and a suitable acid, usually with the addition of a binder or film-forming material, and coating a substrate with such a solution to produce a thin film.

A number of variations of this basic technique may be used and are suggested in the following examples. Other variations no doubt will occur to those skilled in the art.

Among the preferred methods for employing the present compositions is their use in a double-coat system. According to this method, separate solutions of the dicyandiamide and the light-sensitive diazonium salt and acid are prepared and superimposed discrete films are produced on a substrate from each of the solutions.

According to another embodiment, the substrate may be impregnated with the solution of the dicyandiamide and may then be coated with a solution of the light-sensitive diazonium salt and acid.

In making copies by use of the present materials, elements prepared according to any of the foregoing methods are first exposed to light, as, for example, by exposure to ultra-violet radiation through an intermediate master. The unexposed portions of the element are then developed by heating, as, for example, by being placed in an oven or by being exposed to radiation from a quartz infrared lamp. With the present compositions, images are developed by heating to a temperature of from 120 150 C.

In this manner, stable images are produced which are characterized by sharpness, depth of color and good contrast with the background. Very importantly too, diazo elements prepared from our compositions may be stored under high relative humidity conditions for extended periods of time without deteriorating, unlike other known diazo materials.

The theory underlying the surprising performance and usefulness of the compositions of the present invention is not entirely clear. However, we know that upon heating to 120150 C. a coupler is produced. This coupler, in turn, enters a coupling or color forming reaction with the diazo salt.

Thus, the coupler is not present in the composition until the moment of development, at which time it is generated in situ by thermolytic reaction of the ingredients. This completely avoids the problem of premature coupling and poor shelf life in high humidity environments.

The in situ generation of a coupler in this manner, purely by the application of heat, also eliminates the need for the application of a separate coupler.

A further feature of the invention stems from the fact that no adjustment of the pH of the system is necessary in order to bring about color formation. Heat alone is sufiicient to develop the composition and so no ammonia or other developer need be applied.

In specific formulations, operable ranges for the essential ingredients of the present composition comprise from 0.1 percent to 10 percent of a light-sensitive diazonium salt, from 0.1 percent to 35 percent dicyandiamide and from 0.1 percent to 25 percent of a polycarboxylic acid, the balance being non-essential additives, such as film forming resins and polymers, antioxidants, stabilizers and other materials common in the art.

The invention will perhaps be better understood in connection with the following detailed examples of practicing the invention including preparing the compositions, applying them to substrates, and utilizing them to produce copies.

Example 1 10 grams of cellulose acetate-butyrate, viscosity onehalf second, are dissolved in 100 ml. of methyl alcohol. The mixture is warmed on a steam bath to accelerate the solution. To this solution are then added grams of malic acid, one gram of dicyandiamide and two grams of l-N-morpholino 4-diazo 2,5-diethoxy benzene, one-half zinc chloride salt.

A Myler film support is then thinly coated with the foregoing solution forming an adherent film on the Mylar. The coated element is then exposed to ultra-violet light through a positive transparency for approximately twenty seconds. After exposure, the element is heated for thirty seconds at from 120150 C., whereupon a stable reddish-brown positive image is formed.

Example 2 4 grams of colloidal silica are suspended in 100 ml. of water. The following materials are then added to this suspension: 5 grams malonic acid, 2 grams naphthalene 1,3,6-trisodium sulfonate, a stabilizer, and one gram p-diazo ethyl hydroxyl ethyl aniline one-half zinc chloride salt.

Next, a paper support is thoroughly wetted with a saturated aqueous solution of dicyandiamide and is then dried. The treated paper is then coated with a solution as described above and is dried.

The prepared element is exposed to ultra-violet light under a positive transparency for about four seconds and is heated for approximately thirty seconds at from 120- 150 C. producing a stable, red positive image.

Example 3 15 grams of dicyandiamide and 10 grams of cellulose acetate butyrate, viscosity one-half second, are dissolved in ml. of ethylene glycol monomethyl ether. This solution is coated on a support and allowed to dry.

A second solution is prepared by dissolving 10 grams of cellulose acetate butyrate, viscosity one-half second, in 100 ml. of methyl alcohol with gentle warming and then adding to this solution 10 grams citric acid, 5 grams thiourea and 1 gram p-diazo-N-methyl-N-hydroxyethylaniline one-half zinc chloride. A coating of this solution is then formed on top of the initial coating and is also dried.

The element obtained in this manner is then exposed to ultra-violet light under a positive transparency for approximately six seconds. Upon heating for thirty seconds at from -150 C., a stable violet image is produced.

Example 4 10 grams of dicyandiamide and 2 grams of cellulose acetate butyrate, viscosity twenty seconds, are dissolved in a 100 ml. of ethylene-glycol-monomethyl ether. This solution is coated on a paper support and allowed to dry.

A second solution is prepared by dissolving 5 grams of maleic acid, 2.5 grams aluminum sulfate and 2 grams p-diazo diethylaniline borofluoride in 100 ml. of a water emulsion of polyvinyl acetate. The second solution is then coated over the film derived from the first solution to produce a doubly coated substrate.

The foregoing element is then exposed to ultra-violet light under a positive transparency for six seconds and is heated for thirty seconds at from 120150 C., forming a stable brown image.

While there have been shown and described and pointed out fundamental novel features of the invention as applied to the preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A light sensitive, heat developable diazonium composition free from a separate active coupling component until such time as heat is applied comprising a light sensitive diazonium salt, dicyandiamide, and a polycarboxylic acid selected from the group consisting of citric, maleic and malonic acids.

2. A light sensitive heat developable diazonium composition free from a separate active coupling component until such time as heat is applied comprising a film forming resinous base,

from 0.1 percent to 10 percent by weight of alight sensitive diazonium salt,

from 0.1 percent to 35 percent by weight of dicyandiamide and from 0.1 percent to 25 percent by weight of a polycarboxylic acid selected from the group consisting of citric, maleic and malonic acids.

3. A light sensitive seat developable element free from a separate active coupling component until such time as heat is applied comprising a heat stable substrate and a coating on the surface of said substrate comprising a light Ii or sensitive diazonium salt, dicyandiamide, a polycarboxylic acid selected from the group consisting of citric, maleic, and malonic acids, and a film forming material.

4. A light sensitive heat developable element free from a separate active coupling component until such time as heat is applied comprising a heat stable substrate impregnated With dicyandiamide and a coating on said substrate comprising a light sensitive diazonium salt and a polycarboxylic acid selected from the group consisting of citric, maleic and malonic acids.

5. A light sensitive heat developable element free from a separate active coupling component until such time as heat is applied comprising a heat stable substrate,

one coating on said substrate comprising dicyandiamide, a second discrete coating on said substrate, contiguous with said first coating comprising a light sensitive diazonium salt and a polycarboxylic acid selected from the group consisting of citric, maleic and malonic acids. 6. A light-sensitive heat developable element free from a separate active coupling component until such time as heat is applied comprising a heat stable substrate, one

" coating on such substrate comprising from 0.1% to 35% by weight of dicyandiamide and a second discrete coating on such substrate contiguous with said first coating comprising a light-sensitive diazonium salt and from 0.1% to by weight of a polycarboxylic acid selected from the group consisting of citric, maleic and malonic acid.

7. A light-sensitive heat developable element free from a separate active coupling component until such time as heat is applied comprising a heat stable substrate impregnated with from 0.1 to by Weight of dicyandiamide and a coating on such substrate comprising a light-sensitive diazonium salt and from 0.1% to 25% by Weight of a polycarboxylic acid selected from the group consisting of citric, maleic and malonic acid.

References Cited in the file of this patent UNITED STATES PATENTS 1,822,065 Sprongerts et al. Sept. 8, 1931 2,593,911 Neumann et al Apr. 22, 1952 2,662,013 Sulich et al Dec. 8, 1953 2,709,655 Frederick May 31, 1955 2,732,299 Morrison Jan. 24, 1956 3,046,128 Klimkowski et al. July 24, 1962 FOREIGN PATENTS 816,601 Great Britain July 15, 1959 

3. A LIGHT SENSITIVE SEAT DEVELOPABLE ELEMENT FREE FROM A SEPARATE ACTIVE COUPLING COMPONENT UNTIL SUCH TIME AS HEAT IS APPLIED COMPRISING A HEAT STABLE SUBTRATE AND A COATING ON THE SURFACE OF SAID SUBSTRATE COMPRISING A LIGHT SENSITIVE DIAZONIUM SALT, DICYANDIAMIDE, A POLYCARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF CITRIC, MALEIC, AND MALONIC ACIDS, AND A FILM FORMING MATERIAL. 